Earth Planets Space, Vol. 61 (No. 7), pp. e33-e36, 2009E-LETTER
Masayuki K. Yamamoto1, Toyohisa Kishi1, Takuji Nakamura1, Noriyuki Nishi2, Mamoru Yamamoto1, Hiroyuki Hashiguchi1, and Shoichiro Fukao1, 3
1Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Uji, Kyoto 611-0011, Japan
2Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
3Fukui University of Technology, Fukui 910-8505, Japan
(Received August 27, 2008; Revised July 16, 2009; Accepted July 18, 2009; Online published August 7, 2009)
Using a 46.5-MHz atmospheric radar referred to as the MU radar (MUR) and a Raman/Mie lidar installed at the Shigaraki (34°51'N, 136°06'E), continuous wind motions around the tops of the midlatitude cirrus are described for the first time. The cloud system extended from the northeast to southwest (35°N-50°N) along the eastward-moving trough and passed over Shigaraki in the nighttime between 5-6 November 2004. Cloud-top altitude observed by the lidar was located at ∼10.6 km around 1900 LST 5 November, then gradually descended to ∼8.4 km around 0500 LST 6 November. The westerly wind observed by MUR with 12-min and 150-m resolutions showed a rapid increase with altitude around the cloud tops and was almost always larger than 25 m s-1 above ∼1 km higher than the cloud tops. Objective reanalysis showed that a subtropical jet whose core existed to the south of Shigaraki caused a synoptic-scale vertical increase in the westerly wind around the cloud tops. Radiosondes observed a significant vertical increase of potential temperature (greater than 4 K within several hundred meters) around the cloud tops. MUR successfully observed fine time and altitude variations of winds which showed a good correspondence with the descending cloud tops.
Key words: Radar, lidar, cirrus.